1. Field of the Invention
The invention relates to a method of fabricating an opening, and more particularly to a method of fabricating an opening formed by deep ultra-violet photoresist (DUV PR).
2. Description of the Related Art
Deep ultra-violet photoresist is necessary for the semiconductor process with the size of 0.25 .mu.m or less. It can be employed in, for example, oxide layer etching. The DUV PR is exposed under a deep ultra-violet light and developed to define the oxide layer. An opening for a contact, via or damascene is then formed by developing the DUV PR. DUV PR is used to reduce the width of the opening but the material of the DUV PR is soft and not high temperature compatible. Thus erosion and reflow of the DUV PR easily occurs while etching the oxide layer which requires high ion energy. Thus, the side profile of the DUV PR isn't entirely vertical and it is difficult to precisely control the width of the opening. A commonly employed method of preventing overetching of the DUV PR is to increase the thickness of the DUV PR. However, the increment of the thickness prevents the photoresist from being properly exposed and successfully developed, because of focus of depth. Therefore increasing the thickness of the DUV PR as described above doesn't solve the problem.